[D] Test set perfomace metrics better than cross validated train set metric

I have a very limited biological dataset with the dimensions like 200 x 700. I am making regression models with 170 train data and 30 in test data. Main the cross validated models in caret give me performance that are about 50% lower( r2, RMSE mae) than when i test my model on the test set. I understand that that this might be due to bad data split with the test set having 'simpler' samples and the data is obviously …

machinelearning metrics set test